The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
The I.E.E.E. has defined various standards for configuring wireless networks and devices. For example, 802.11, 802.11(a), 802.11(b), 802.11(g), 802.11(h), 802.11(n), 802.16, and 802.20. According to these standards, wireless network devices may be operated in either an infrastructure mode or an ad-hoc mode. In the infrastructure mode, the wireless network devices or client stations communicate with each other through an access point. In the ad-hoc mode, the wireless network devices communicate directly with each other and do not employ an access point.
Referring now to FIG. 1, a first wireless network 10 is illustrated in an infrastructure mode. The first wireless network 10 includes one or more client stations 12 and one or more access points (AP) 14. The client station 12 and the AP 14 transmit and receive wireless signals 16. The AP 14 is a node in a network 18. The network 18 may be a local area network (LAN), a wide area network (WAN), or another network configuration. The network 18 may include other nodes such as a server 20 and may be connected to a distributed communications system 22 such as the Internet.
Referring now to FIG. 2, a second wireless network 24 operates in an ad-hoc mode. The second wireless network 24 includes multiple client stations 26-1, 26-2, and 26-3 that transmit and receive wireless signals 28. The client stations 26-1, 26-2, and 26-3 collectively form a LAN and communicate directly with each other. The client stations 26-1, 26-2, and 26-3 are not necessarily connected to another network.
To minimize radio frequency (RF) interference, some wireless networks may operate in a 5 GHz band. However, regulatory requirements governing the use of the 5 GHz band vary from country to country. For example, some countries utilize the 5 GHz band for military radar communications. Therefore, wireless networks operating in the 5 GHz band generally employ dynamic frequency selection (DFS) to avoid interference with radar communications. Specifically, wireless network devices generally employ DFS to switch to a different channel of the 5 GHz band to avoid interfering with radar communications.
In infrastructure mode, the AP 14 transmits beacons to inform the client stations 12 that the AP uses DFS. When the client stations 12 detect radar on a channel, the client stations 12 notify the AP 14. Based on this information, the AP 14 uses DFS to select the best channel for network communications that will not interfere with radar.
In ad-hoc mode, one client station may be designated as a DFS owner. The DFS owner is responsible for collecting information from other client stations. If any client station in the ad-hoc network detects radar, the DFS owner uses DFS to select the best channel for network communications that does not interfere with radar. For example, if station 26-1 is the DFS owner, it is responsible for collecting information from stations 26-2 and 26-3. If any of the stations 26-1, 26-2, and 26-3 detects radar, station 26-1 uses DFS to select the best channel and notify stations 26-2 and 26-3 to switch to that channel.
Referring now to FIGS. 3A-3C, radar signals generally comprise bursts of pulses that have predetermined pulse widths and pulse repetition rates. FIG. 3A shows a burst of radar. Radar signals can be tone or chirp type. Frequency of tone type radar pulses is generally fixed, whereas frequency of chirp type radar pulses may vary linearly. Based on characteristics such as pulse width (PW), pulse repetition rate (PRI), etc., radar signals may be classified into different types. For example, a table in FIG. 3B shows types of radar signals and respective standards specified by the federal communications commission (FCC). Similarly, a table in FIG. 3C shows types of radar signals and respective standards specified by the European telecommunications standards institute (ETSI).